Hi there Erik,
We understand you're having some trouble pairing your existing Bluetooth devices with your new iPhone, and we'll be happy to help.
Are you still in possession of your iPhone 8? If so, try removing the device from Bluetooth settings there, then attempt setting it up on your new iPhone again. The "Unpair a Bluetooth accessory" section of the following page explains how: Pair a third-party Bluetooth accessory with your iPhone, iPad, or iPod touch
If there's no change, or you no longer have your previous iPhone, consultant the documentation that came with the device, or contact the manufacturer to see whether there's a reset process. After resetting, attempt to pair the device again.
Additional information about pairing this specific type of device can be found here: Use Made for iPhone hearing devices
We hope this helps!